sedimentary
Chert (Flint)
Silicon dioxide (SiO2)
Hardness: 7 (Mohs); Color: Grey, blue-grey, or black; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline); Cleavage: None (Conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 (Mohs)
- Color
- Grey, blue-grey, or black
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs); Color: Grey, blue-grey, or black; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline); Cleavage: None (Conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of siliceous remains of marine organisms (diatoms, radiolarians) or by chemical precipitation from silica-rich fluids in limestone or chalk beds.
Uses & applications
Historically used for stone tools and starting fires; currently used as a road aggregate, in jewelry (as jasper/agate varieties), and for flintlock mechanisms.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges for knives and arrowheads.
Field identification & locations
Identify by its extreme hardness (scratches glass), waxy appearance on fresh surfaces, and characteristic 'shell-like' curved fracture patterns. Commonly found in nodules within limestone.
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